Field of the Invention
The present invention relates to a mirror driving device, and particularly, a structure of a micro-mirror device suitable for an optical deflector to be used for optical scanning, and relates to a driving method therefor.
Description of the Related Art
A micro-scanner (hereinafter, referred to as a “MEMS (Micro Electro Mechanical System) scanner”) made using a fine processing technology for silicon (Si) is characterized in that it has a small size and a low power consumption compared to a polygon mirror, which is a conventional optical scan module, and the like. Therefore, the MEMS scanner is expected to be widely applied, for example, to a laser projector, and a scanner for optical diagnostics such as optical coherence tomography (OCT).
As the structure of the MEMS scanner, a torsion bar system shown in Japanese Patent Application Laid-Open No. 2011-150055 (PTL 1), Japanese Patent Application Laid-Open No. 2008-40240 (PTL 2) and the like is typical. In this system, two, or three or more torsion bars supporting a mirror are twisted. Thereby, the mirror is inclined, and the optical scan is performed. For actualizing a specially large scan angle, a resonant drive is performed. In this case, the structure design is performed such that the resonant frequency of the inclining motion of the mirror coincides with the frequency of the drive.
Further, for the drive of the MEMS scanner, there is known a configuration in which an angle sensor capable of sensing the angle of the mirror is provided for the purpose of monitoring the angle of the mirror and maintaining a resonance state. As for conventional MEMS scanners with the torsion bar system, there are proposed a configuration in which an angle sensor utilizing the piezo-resistance effect is provided at a base portion of the torsion bar (“JOURNAL OF MICROELECTROMECHANICAL SYSTEMS”, Vol. 15, No. 4, August 2006, (NPL 1)), and a configuration in which an angle sensor utilizing the piezoelectric effect of the a piezoelectric thin film is used (T. Iseki et. al., IEEJ Trans. Elec. Electron. Eng. 2010, 5, pp. 361-368, (NPL 2)), and some has been put to practical use.